Section 27-428. Ventilation

Mechanical  ventilation  systems  in moderate
  hazard plants shall be adequate to effect ten complete air  changes  per
  hour.    Low  hazard  dry cleaning establishments shall be provided with
  mechanical ventilation adequate to effect four complete air changes  per
  hour.    Ventilating  systems  shall  be  arranged  in such manner as to
  prevent solvent vapors from being admitted to the combustion area of any
  device  requiring  an  open  flame.  Sufficient  make-up  air  shall  be
  introduced  into  all  parts  of  the  establishment  to  equal  the air
  exhausted by the dry cleaning units,  dryers,  and  exhaust  ventilating
  system.  Such  air  shall  not contain any flammable vapors. Openings or
  stacks discharging solvent vapor-air mixtures to the outdoors  shall  be
  located in accordance with the provisions of subchapter thirteen of this
  chapter.